In a mobile communication system, if a building is built in the vicinity of a base station, or if the installation status of a base station in the vicinity of the base station changes, the radio environment related to the base station changes. Therefore, conventionally, an operator performs a drive test of measuring a radio environment by using a measurement vehicle provided with a measurement equipment, and collecting a measurement result and location information at the time of the measurement.
Such a method, for example, may contribute to the optimization of the coverage of abase station, but faces the problem of too many man-hours and high cost. In this regard, according to 3GPP (3rd Generation Partnership Project) which is a project aiming to standardize a mobile communication system, a radio terminal owned by a user is used to proceed with the specification design of MDT (Minimization of Drive Test) which is a technology for automation of the measurement and collection (refer to Non Patent Literatures 1 and 2).
As a type of the MDT, there is an immediate report-type MDT (hereinafter, appropriately referred to as “Immediate MDT”). According to the Immediate MDT, a radio terminal in a connected state (a connected mode) performs measurement according to a parameter set from a network, and reports a measurement result and location information to the network. Furthermore, the connected state indicates the state in which the radio terminal performs communication.
Furthermore, as a type of the MDT, there is a record-type MDT (hereinafter, appropriately referred to as “Logged MDT”). According to the Logged MDT, a radio terminal in an idle state (an idle mode) performs measurement of a radio environment according to a parameter (a measurement condition) set from the network, records a measurement result as measurement data together with location information (and time information), and reports the measured measurement data to the network later. Furthermore, the idle state indicates the state (for example, during standby) in which the radio terminal interrupts communication.
In the MDT, since a plurality of radio terminals perform measurement under various conditions, it is considered that measurement data important for the network and unimportant measurement data coexist.
However, in the MDT, since the radio terminal records a measurement result as measurement data and reports all types of obtained measurement data to the network in all cases in which a radio environment or the state of the radio terminal satisfies the measurement condition, it is probable that the network (that is, an operator) is not able to sufficiently collect important measurement data. Furthermore, when a large amount of unimportant information is included, it is also probable that the network recognizes a problem other than a true problem as an important problem and performs inappropriate optimization.